A wastewater bypass solution in Parnell that will significantly reduce overflows into the Waitematā Harbour is now operational after a massive 20-day effort to get it planned and built in record time.

The temporary pump station on St Georges Bay Rd

Watercare began work on the bypass on Thursday September 28, after a sinkhole formed above the Ōrākei Main Sewer and the pipe was blocked when the land caved in.

Watercare chief operations officer Mark Bourne says: “It’s been a monumental effort from our staff, contractors and suppliers to get the bypass planned, the pipes laid, the pump station chamber excavated and concreted, and have six large temporary pumps installed and tested.

“Normally this type of project would take several months to deliver, so I’m incredibly proud of the whole team involved for their hard work and dedication to this critical project.

“Knowing that this work was vital to prevent the high-volume overflows into the Waitematā Harbour has been a huge motivator for everyone involved. I’d like to pass on our sincere thanks to those inside and outside of Watercare who have helped us along the way.”

The temporary pump station can handle flows up to 600 litres per second.

“We expect that this will be sufficient to handle normal flows in dry weather. But these temporary pumps are more susceptible to blockages than our standard network pumps, so it will be more important than ever for people to only flush the 3Ps – pee, poo and toilet paper. Please don’t flush wet wipes or any other rubbish,” Bourne says.

“Just as there was prior to the sinkhole developing, in wet weather, in wet weather, there will still be overflows into the Waitematā Harbour. This is because some of the catchments that feed into the Ōrākei Main Sewer are historic combined stormwater/wastewater catchments. Overflows from these combined networks are commonplace in wet weather, but they will be more frequent than normal until we have wastewater flowing through the Ōrākei Main Sewer again.

“For now, the rāhui put in place by Ngāti Whātua Ōrākei for the inner Waitematā Harbour remains in place,” Bourne says. “We’ll continue to encourage people to check safeswim.org.nz for the latest water quality information before they head into the harbour.”

Environmental monitoring

Watercare has sought the advice of marine environmental experts, Ngāti Whātua Ōrākei and other mana whenua, and is following their recommendations with a monitoring programme to assess the impact of the overflows on the Waitematā Harbour.

“In addition to the widespread sampling undertaken since the first week of the overflows by Auckland Council’s Safe Networks and Safeswim teams, we began a targeted daily harbour sampling regime on Wednesday October 11. These samples are being taken at multiple sites and depths and are being tested for a wide range of parameters,” Bourne says.

“We are also placing bags of oysters at locations from Westhaven to Okahu Bay. Samples from these bags will be tested every fortnight for bacteria and heavy metals. This information will supplement our data from the water sampling programme.”

Watercare will also be carrying our routine beach inspections. So far there has not been any noticeable wastewater debris on beaches.

“We’ve engaged the Sea Cleaners Trust to carry out routine inspections of the harbour and report back to us. So far, they haven’t seen any more debris in the harbour than they normally would.”

Repairing the damaged Ōrākei main sewer

With the wastewater bypass now operational, Watercare’s focus will turn to the plan to clear the remaining boulders blocking the Ōrākei Main Sewer and carry out the necessary rehabilitation to the sewer.

“We’ve been clearing the loose debris from the blockage by hydro-jetting 24/7 over the past few weeks, but what’s left in the pipe is large boulders that can’t be removed with this method,” Bourne says.

“We’re now planning how we can safely remove these boulders. We’re also firming up our plan for the rehabilitation of the section of the Ōrākei Main Sewer that’s been damaged.

“We think it could take about six months to complete this rehabilitation work. However, we expect to have wastewater flowing through the pipe again once the blockage is cleared. The work to reline the sewer can be carried out with the pipe in service.”

Cause of sinkhole under review

Watercare is in the process of engaging an engineering consultancy to review the cause of the Parnell sinkhole and subsequent Ōrākei Main Sewer blockage.

Watercare chief executive Dave Chambers says the comprehensive review will look at all data from the sinkhole site, as well as Watercare’s historical and planned maintenance and condition assessment programmes.

“We want to find out what happened and if there’s anything that could have been done differently to prevent the sinkhole from occurring and the resulting overflows to the harbour.

“We expect the review will take several months, and we will publish the report when it’s available.

“The Waitematā Harbour is a taonga and to have these high-volume overflows going into the harbour has been terrible and understandably upsetting to many Aucklanders, as it has been to our staff. We’d like to thank Aucklanders for their patience while we’ve worked to put this bypass in place.

“We’d also like to thank our construction partners, Ngāti Whātua Ōrākei, Deputy Mayor Desley Simpson and the Waitematā Local Board for their support, and of course the local businesses and residents impacted by this work.”

B-roll footage: https://vimeo.com/875001940

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